1. Field of the Invention
The subject of the present invention is an optical system for a motor vehicle having a stylized main function, performed by means of at least one light source, in particular of the light-emitting diode type. The essential purpose of the invention is to propose, on the basis of a limited number of light sources, preferably LEDs, an optical system performing a main optical function by means of a transmission screen, the visible surface of which is sufficient to satisfy the regulatory requirements of the optical function under consideration. The term optical system refers to an element forming part or all of a headlamp device, exhibiting at least one light source and means of performing at least one optical function; optical function refers to the production of a regulatory light beam for the production of certain of the lights mentioned below.
The domain of the invention is, in general, that of the lights or lamps of motor vehicles. In this domain, various types of lights are known, among which are included essentially:                tail lights, or position lights, of low intensity and range;        low beam lights, or dipped lights, of higher intensity and with a range on the road in the vicinity of 70 meters;        long-range high-beam headlamps, and additional lights of the long-range type, with a zone of vision on the road in the vicinity of 200 meters;        advanced headlamps, known as dual-mode, which combine the functions of dipped headlights and full beam headlights by incorporating a detachable mask;        fog lamps;        signalling lights, in particular front and rear turn indicators, reverse lights, or tail lights;        signalling devices of the position light type for daytime use, known as DRL (Daytime Running Light) devices.        
The domain of application of the invention is essentially that relating to brake lights, turn indicators, position lights or DRL.
2. Description of the Related Art
For all of these headlamps and lights, the light sources traditionally used are of the halogen lamp type, or discharge lamps. But for some years now, automotive equipment suppliers have proposed the utilization of light-emitting diodes, or LEDs; this utilization concerns, for example, indicator lights or rear lights.
Light-emitting diodes present a certain number of advantages:                first of all, for a long time, it has been known that this type of diode does not send out beams omnidirectionally, but radiates in a half space opposite a substrate which supports the P-N junction of the diode considered; thus, by using radiation more directionally than halogen or discharge lamps, from the state of the art, the quantity of energy wasted is less than with discharge or halogen lamps;        further, these diodes have recently been improved in terms of the intensity of radiated power. Moreover, manufactured diodes have for a long time emitted radiation in red, but now also in white, which expands the field of their potential uses. The amount of heat which they give off is relatively limited, and a certain number of constraints, in connection with the dissipation of heat in state of the art headlamp devices, no longer apply; the problem of heat dissipation, however, remains important for power LEDs;        finally, diodes consume less energy than discharge or halogen lamps, even at the same radiation intensity; they take up little space, and their particular shape offers new possibilities for the creation and the configuration of the complex surfaces associated with them, in particular by arranging them on electronic supports of the flexboard type.        
The use of LEDs has become more and more widespread, in particular to respond to the aesthetic criteria desired by vehicle manufacturers. This use especially enables the production of headlamps presenting original volumes, for example by arranging LEDs three-dimensionally, i.e. on a non-plane support substrate, within the headlamp devices in question, or again, by using light guide type elements.
Furthermore, an optical system has recently been proposed in which different LEDs were specifically used to create a curtain of light by means of a screen inside the optical system, in which the light produced by the diode or diodes is propagated, the optical system also performing an optical function, known as the main optical function by comparison with any other optical function which may be performed by the optical system in question, in the form of a light beam generated by a third light source. In this optical system, it is necessary to make use of a plurality of light sources, as the LEDs used are not involved in the performance of the main optical function. The cost of such an optical system is therefore high, due to the large number of light sources it requires, and, for the same reasons, it takes up a lot of space.
The term curtain of light refers to a surface illuminated by part of an optical system, the illumination being produced by light beams circulating inside a volume, in particular delimited by the illuminated surface, the illumination having until then a purely decorative function, not executing, or not contributing to—or only insignificantly—the performance of the main optical function. Advantageously, the illumination produced is as continuous as possible, with no pixelization effect.